Well, with the tech stop eliminated, you're guaranteed to lose some slots, so you have to re-buy them anyway.
I'm asking for the possibility of going from "Open route - A via B to C" to "Open route - A to C" without doing
- go to the current 1 stop route
- close route, click on "keep slots"
- open new route
Again, yes, you will lose the slots, either at A or C, but you'd lose the slots anyway if you open the nonstop route in a different window.